UNIT – 6 Fundamentals of Agronomy 4(3+1)

Growth and development of crops

Plant Growth

• Definition: Irreversible, quantitative increase in size, mass, and/or volume of a plant or its parts.
• Energy: Requires expenditure of metabolic energy.
• Examples:
  • Leaf formation
  • Increase in plant height etc.
• Quantification Methods of plant growth: Cell number, fresh weight, dry weight, plant height, length, width, area, and volume (each with limitations).

Processes:

• Combined effect of cell division and cell enlargement.
• Growth can occur without cell division and vice versa.

Early Embryo Growth: Quantified by increase in cell number, despite small cell size not increasing embryo size.

Plant Development

• Definition: Various changes during a plant’s life cycle, including both growth and differentiation.
• Changes: Involves quantitative and qualitative changes.
• Characteristics:
  • Change in size, shape, form, degree of differentiation, and state of complexity.
• Relationships:
  • Growth can occur without differentiation.
  • Differentiation can occur without growth.

Factors Affecting Growth and Development

General Factors

1. Genetic Factors (Internal)

• Basis of plant expression (genes) located within the cell.
• Determines plant characteristics.

1. Environmental Factors (External)

• Divided into biotic (living) and abiotic (non-living) components.
• Influences the extent of genetic expression.

Abiotic Factors

1. Climatic Factors

• Rainfall and Water:
  • Critical for plant growth.
  • Determines yield success or failure.
  • Plants adapted to various water conditions (mesophytes, hydrophytes, xerophytes).
• Light:
  • Essential for chlorophyll production and photosynthesis.
• Temperature:
  • Influences photosynthesis, respiration, transpiration, seed dormancy, germination, protein synthesis, and translocation.
  • Optimal range for plant survival: 0 to 50°C.
• Air:
  • Oxygen essential for respiration.
  • Carbon dioxide crucial for photosynthesis.
• Relative Humidity:
  • Affects stomatal activity and transpiration.
  • High humidity conditions used for plant propagation.
• Wind:
  • Moderate winds favor gas exchange.
  • Strong winds can cause water loss and physical damage.

Growth Curve – Planta show sigmoid growth curve.

• Sigmoid Growth Curve (S-shaped)
• Lag Phase: Slow initial growth.
• Exponential Phase: Rapid growth.
• Stationary Phase: Growth rate decreases due to nutrient limitations.

Parameters Used in Growth Analysis

1. Leaf Area Index (LAI)

• Importance: Indicates photosynthesis potential and growth.
• Definition: Ratio of one-sided leaf area to ground area.
• Formula:
• LAI =Total leaf area for a given land area /Land area considered

2. Crop Growth Rate (CGR)

• Importance: Indicates the rate of crop growth (faster or slower than normal).
• Definition: Rate of dry matter production per day.
• Formula:
  CGR= (W2 – W1)/(t2 – t1)
  where ( W2 ) and ( W1 ) are the final and initial dry weights at times ( t2 ) and ( t1 ) respectively.
• Units: g/m²/day.

3. Relative Growth Rate (RGR)

• Importance: Rate of growth per unit dry matter.
• Definition: Dry matter produced by a g of existing dry matter in a day, similar to compound interest.
• Units: g/g/day.

4. Net Assimilation Rate (NAR)

• Importance: Indicates rate of net photosynthesis.
• Definition: Dry matter produced per dm² of leaf area in a day.
• Units: g/m²/day.
• Note: Uses leaf area of individual plants, not leaf area index.

5. Leaf Area Duration (LAD)

• Importance: Measures a crop’s ability to produce leaf area over its life cycle.
• Definition: Function of leaf area, net assimilation rate, and duration of leaf area.
• Units: Days.

UNIT –7 Plant ideotypes, crop rotation and its principles, adaptation and distribution of crops, crop management technologies in problematic areas.